The embodiments herein generally relate to mobile television (TV) technologies, and, more particularly, to transmission schemes for mobile TV digital video broadcasting (DVB) applications.
Handheld devices with integrated digital television access are a relatively new phenomenon. Such technology has traditionally been limited by size, power consumption, and most importantly performance. Poor performance of such devices has typically been the result of the constantly changing receiver environment. More particularly, the quality of the received signal is affected by the device's ability to manage adjacent-channel rejection, low signal-to-noise ratios, and Doppler compensation, among other factors.
Digital Video Broadcasting-Handheld (DVB-H) is the specification for bringing broadcast services to handheld receivers, and was formally adopted as an ETSI (European Telecommunications Standards Institute) standard in November 2004. More specifically, DVB-H is a terrestrial digital TV standard that tends to consume less power than its predecessor, the DVB-T standard, and generally allows the receiver to move freely while receiving the signal transmission, thereby making it ideal for cellular phones and other mobile devices to receive digital TV broadcasting over the digiTV network, and hence without having to use cellular telephone networks.
In mobile TV DVB-H systems such as DVB-H (ETSI EN 301 192), one radio frequency (RF) channel is shared among many TV channels (TV programs). These TV channels are multiplexed in the time domain. Each channel is given full access to the entire RF channel bandwidth for a short period of time (burst duration). After that data burst is transmitted, bursts for other channels occupy the RF channel and so on. This multiplexing process is called time division multiplexing (TDM).
FIG. 1 shows an example of time division multiplexing of 15 TV channels on one RF channel. In FIG. 1, the TV channels are labeled 1, 2, 3, . . . , 15. As shown in FIG. 1, each TV channel occupies the entire RF channel for
  1  15of the time. A receiver which is watching only one channel (for example, channel 2) only has to be active (ON) during the periods of channel 2 bursts. In order to conserve battery consumption, such a receiver will typically turn off its circuits when channel 2 bursts are not occupying the RF channel. Thus, the receiver enters into a SLEEP mode. This suggests that the TDM of channels can help reduce power consumption of a receiver watching a single channel. For the channel line up depicted in FIG. 1, each burst contains five seconds (cycle time) of encoded video.
In DVB-H systems, the burst size allocated to each channel is fixed (for example, 2 Mbit). It is also common to use forward error correction (FEC) to protect the transmitted burst against fading of the wireless channel. FIG. 2 shows a FEC scheme in DVB-H. Encoded video is transmitted in the form of Internet Protocol (IP) datagrams. The IP datagrams fill what is known as a multi protocol encapsulation (MPE) frame that consists of 191 columns. The data is encoded row wise using a Reed Solomon (RS) code to obtain 64 FEC columns that form a FEC frame. Thus, the MPE frame is approximately 1.5 Mbit and the FEC frame is approximately 0.5 Mbit. Both the MPE and FEC frames form a 2 Mbit MPE-FEC frame. The DVB-H standard allows zero padding of the data, when the data size is less than 1.5 Mbit. In other words, when the data size is less than 1.5 Mbit (for example, the data size is 1.4 Mbit), then ZERO data is added to the real data to actual data such that the total size becomes 1.5 Mbit. In this example 0.1 Mbit of zeros are added; hence the term “zero padding” is used in the context herein. The zero padding bits are not transmitted. Furthermore, the DVB-H specification allows the transmitter to choose to transmit only a subset of the FEC columns. The FEC columns that are not transmitted are called punctured columns. The receiver treats the punctured columns as errors and declares them as erasures in the RS decoding process. Thus, only the hatched portions in FIG. 2 are transmitted to the receiver. For the example given in FIG. 1, the average bit rate of the transmitted video channel is approximately 1.5 Mbit/5 seconds—100 Kpbs. This rate is fixed for all the channels in this example.
The bit rate generated from a video encoder depends on the nature of the video program that is being transmitted on a particular channel. For example, a sports event that generally contains fast motion and a frequently changing picture background typically needs more bits to represent the video than a news channel that has a generally static background, for example. To achieve the same quality of video, the sports channel is assigned a higher bit rate than the news channel. Now, if each channel is assigned the same fixed burst size, then the average bit rate of each channel will be fixed. In order to achieve a given quality standard of video for all programs, the system has to accommodate the worst case channel. In other words, the burst size will be chosen to be adequate for the highest needed bit rate to accommodate the most demanding channel (i.e., demanding in terms of a high data rate). Thus, for the channels that do not need such a high bit rate of the worst case channel, bits have to be wasted by sending null packets or dummy data. FIG. 3 illustrates a transmitter architecture 300 which uses a fixed burst size for all video channels. Accordingly, there remains a need for a new technique that is capable of providing a variable burst size for different video channels.
In view of the foregoing, an embodiment of the invention provides a DVB-H transmitter comprising a plurality of video encoders each having a variable bit rate associated with IP datagrams for each television program broadcast by one RF channel. Preferably, each video encoder is adapted to create the variable bit rate by controlling quantization parameters associated with the particular TV channel to achieve a given picture quality. The transmitter may further comprise a control mechanism operatively connected to the plurality of video encoders, wherein the control mechanism is adapted to measure a fixed total bit rate generated from all of the plurality of video encoders and to fix a uniform video quality standard among all TV channels. Moreover, the transmitter may further comprise a DVB-H encapsulator operatively connected to each video encoder, wherein the DVB-H encapsulator is adapted to apply a MPE section and a FEC section to transmitted IP datagrams.
Preferably, the DVB-H encapsulator is adapted to generate a variable data burst size for each TV channel by adapting the number of MPE columns on a MPE frame and adapting the number of FEC columns for each data burst to retain a constant MPE-FEC rate corresponding to the transmitted IP datagrams. Furthermore, each video encoder is preferably adapted to create the variable bit rate by controlling quantization parameters associated with the particular TV channel to achieve a given picture quality. Additionally, the DVB-H encapsulator is preferably adapted to provide a Delta-t parameter for each data burst independently to convey timing information to a receiver.
Another embodiment provides a a DVB-H transmitter comprising a plurality of video encoders operatively connected to one another, wherein each video encoder corresponds with a separate TV channel, and wherein each video encoder is adapted to receive audio and video (AV) IP datagrams and to generate a variable encoder bit rate corresponding to an AV transmission signal for a particular TV channel; a control mechanism operatively connected to the plurality of video encoders, wherein the control mechanism is adapted to measure a fixed total encoder bit rate generated from all of the plurality of video encoders and to fix a uniform video quality standard among all TV channels; a DVB-H encapsulator operatively connected to the plurality of video encoders, wherein the DVB-H encapsulator is adapted to apply a MPE section and a FEC section to transmitted IP datagrams, and wherein the DVB-H encapsulator is adapted to generate a variable data burst size for each TV channel by adapting the number of MPE columns on a MPE frame and adapting the number of FEC columns for each data burst to retain a constant MPE-FEC rate corresponding to the transmitted IP datagrams; and a multiplexer operatively connected to the DVB-H encapsulator, wherein the multiplexer is adapted to receive the transmitted IP datagrams and generate DVB-H transport stream (TS) data packets.
Preferably, each video encoder is adapted to create a variable encoder bit rate by controlling quantization parameters associated with the particular TV channel to achieve a given picture quality. Moreover, the DVB-H encapsulator is preferably adapted to provide a Delta-t parameter for each data burst independently to convey timing information to a receiver.
Another embodiment provides a method for statistical multiplexing of video channels for DVB-H mobile TV applications, and a program storage device readable by computer, tangibly embodying a program of instructions executable by the computer to perform the method, wherein the method comprises jointly configuring a plurality of video encoders each having a variable bit rate associated with IP datagrams for each television program broadcast by one RF channel. The method may further comprise creating the variable bit rate by controlling quantization parameters associated with the particular TV channel to achieve a given picture quality.
Additionally, the method may further comprise operatively connecting a control mechanism to the plurality of video encoders; generating a fixed total bit rate generated from all of the plurality of video encoders; and generating a fixed uniform video quality standard among all TV channels. Also, the method may further comprise operatively connecting a DVB-H encapsulator to each video encoder; applying a MPE section and a FEC section to transmitted IP datagrams; and generating a variable data burst size for each TV channel by adapting the number of MPE columns on a MPE frame; and adapting the number of FEC columns for each data burst to retain a constant MPE-FEC rate corresponding to the transmitted IP datagrams. Furthermore, the method may further comprise creating the variable bit rate by controlling quantization parameters associated with the particular TV channel to achieve a given picture quality. Moreover, the method may further comprise adapting a Delta-t parameter for each data burst independently to convey timing information to a receiver.
These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.